1. Field of Invention
The present invention relates generally to grinder pumps, and more particularly but not by way of limitation, to a grinder pump having a self aligning cutter assembly that produces effective and efficient grinding of influent materials.
2. Discussion
Grinder pumps are known in the art for grinding large solid or semisolid materials in a liquid media to form a slurry which is pumped by the pump. A typical grinder pump has an axial inlet communicating with a pumping chamber, and its motor driven shaft extends through the pumping chamber into the inlet. Mounted on a proximal end of the shaft is a rotary cutting disk having a plurality of peripheral cutting edges. An annular, ring shaped cutting member is supported at the pump inlet, axially aligned with the motor driven shaft. The shaft supports and rotates the rotary cutting disk within the ring shaped annular cutting member to effect the grinding action of the pump. An example of such a pump is disclosed in U.S. Pat. No. 5,016,825 issued to Carpenter.
The configuration of the rotary cutting disk and the ring shaped annular cutting members initially, and over the life of these members, effectively determines the effectiveness and the efficiency of a grinder pump in performing the grinding function. Generally, the closer in spatial juxtaposition that the cutting edges of a grinder pump can be maintained, the better the cutting and shearing of solids that can be achieved. Also, the better the cutting yields, the lower is the amperage draw of the pump motor; the less occurrence of relay reengagements; and the less time required to grind the solids.
Along these lines, fibers and stringy materials are known to cause difficulties for grinder pumps because such materials present relatively small cross sections and are not readily engageable by the cutting surfaces. This is especially true as cutting wear causes greater radial separation of the cutting edges of the rotary and annular cutters. Further, the realities of achieving tight manufacturing tolerances between cutting edges make it very difficult and expensive to achieve close radial separation of the cutting surfaces when the pump is initially manufactured, and maintaining close radial separation during the operational life of the grinder pump is problematic at best.
There is a need for a grinder pump having very close radial separation of the cutting edges of the cutter assembly, both initially and during the operating life of the grinder pump. It would also be desirable to achieve such close radial separation by means that will provide cost effective manufacturing and maintenance over a long operational life.